Kyung-soon Moon

At strong magnetic fields, double-layer two-dimensional electron-gas systems can form an unusual broken-symmetry state with spontaneous interlayer phase coherence. In this paper we explore the rich variety of quantum and finite-temperature phase transitions associated with this broken symmetry. We describe the system using a pseudospin language in which the layer degree of freedom is mapped to a fictional spin 1/2 degree of freedom. With this mapping the spontaneous symmetry breaking is equivale

We study numerically the motion of vortices in dirty type II superconductors. In two dimensions at strong driving currents, vortices form highly correlated ``static channels.'' The static structure factor exhibits convincing scaling behavior, demonstrating quasi-long-range translational order in the transverse direction. However, order in the longitudinal direction is only short range. We clearly establish the existence of a finite transverse critical current, suggesting strong barriers against

Resonant tunneling between fractional quantum Hall edge states is studied in the Luttinger liquid picture. For the \ensuremath{\nu}=1/3 Laughlin parent state, the resonance line shape is a universal function whose width scales to zero at zero temperature. Extensive quantum Monte Carlo simulations are presented for \ensuremath{\nu}=1/3 which confirm this picture and provide a parameter-free prediction for the line shape.

We study theoretically the parametric down-conversion and squeezing of microwaves using cavity quantum electrodynamics of a superconducting Cooper-pair box (CPB) qubit located inside a transmission line resonator. The nonlinear susceptibility chi2 describing three-wave mixing can be tuned by dc gate voltage applied to the CPB and vanishes by symmetry at the charge degeneracy point. We show that the coherent coupling of different cavity modes through the qubit can generate a squeezed state. Based

We report Monte Carlo studies of the critical behavior of superfluid ${}^{4}$He in the presence of quenched disorder with long-range fractal correlations. Modeling aerogel as an incipient percolating cluster in 3D and weakening the bonds at the fractal sites, XY-model simulations demonstrate an increase in the superfluid density exponent $\ensuremath{\zeta}$ from $0.67\ifmmode\pm\else\textpm\fi{}0.005$ for the pure case to an apparent value of $0.722\ifmmode\pm\else\textpm\fi{}0.005$ in the pres

In a recent experiment, Milliken et al. demonstrated possible evidence for a Luttinger liquid through measurements of the tunneling conductance between edge states in the \ensuremath{\nu}=1/3 quantum Hall plateau. However, at low temperatures, a discrepancy exists between the theoretical predictions based on Luttinger liquid theory and experiment. We consider the possibility that this is due to long-range Coulomb interactions, which become dominant at low temperatures. Using renormalization-grou

The authors propose a graphene-based subwavelength plasmonic switch, in which gating of a surface plasmon polariton is operated by inducing a local plasmon resonance within a $p$-type Si(100) layer. The resulting sharpness of its switching is the main advantage of this device, for example allowing a response to even a modest carrier-density modulation, such as has been demonstrated recently by others. Putting the pieces together here could strongly advance all-optical plasmonic switching applica

Double-layer quantum Hall systems with spontaneous broken symmetry can exhibit a novel many body quantum Hall effect due to the strong interlayer coherence. When the layer separation becomes close to the critical value, quantum fluctuations can destroy the interlayer coherence and the quantum Hall effect will disappear. We calculate the renormalized isospin stiffness ${\ensuremath{\rho}}_{s}$ due to quantum fluctuations within the Hartree-Fock-RPA formalism. The activation energy of the topologi

We numerically study the interacting quantum Hall Skyrmion system based on the Chern-Simons action. By noticing that the action is invariant under global spin rotations in the spin space with respect to the magnetic field direction, we obtain the low-energy effective action for a many-Skyrmion system. Performing extensive molecular dynamics simulations, we establish the thermodynamic phase diagram for a many-Skyrmion system.